Mets' Josh Thole reacts by flipping his bat in the air after striking out in the eighth inning. Photo: JASON SZENES/NY POST

Collin McHugh walked off the mound toward the dugout after the seventh and final inning of his first major league appearance, tried to remain stone-faced and raised his right hand to touch his cap for the 13 family and friends watching from the stands.

“It was still a tight game so I don’t want to do anything crazy,” he said.

McHugh had a dazzling debut on yet another dismal day for the New York Mets. The 25-year-old right-hander allowed two hits, struck out nine and walked one in seven shutout innings. It wasn’t enough, and the Colorado Rockies completed their second straight four-game sweep at New York with a 1-0 victory Thursday as Jordany Valdespin misplayed Tyler Colvin’s leadoff drive in the eighth into a game-changing triple.

New York was 0 for 10 with runners in scoring position in the game and 8 for 43 (.186) in the series. The Mets have been held to two runs or fewer for six straight games for the first time since a streak of seven in a row from Sept. 17-21, 1982, according to STATS LLC.

Collins admitted he’s turned his attention to 2013.

“At this stage of the season, you’ve got to start looking to next year, you’ve got to start looking at the big picture,” he said, pleased with some of his young pitchers such as Matt Harvey and McHugh. “You look for Sept. 1 now to say who’s going to be the next guy that’s going to whet our tastebuds?”

New York is 11-28 since the All-Star break, which includes a 2-14 mark at Citi Field, and is 11 games under .500 for the first time since finishing 70-92 in 2009.

“It’s a nightmare for everybody in this clubhouse,” catcher Josh Thole said.

“When it happens once, OK. When it happens again, all right guys, you’ve got to move on. But three nights in a row. And then four. And then it keeps mounting up. You can only say we’ve got to put this behind us so many times,” he said.

Taking the rotation slot of injured ace Johan Santana, McHugh threw 63 of 100 pitches for strikes. After Charlie Blackmon’s opposite-field double to left leading off the game, McHugh retired 20 of 22 batters around D.J. LeMahieu’s double starting the third and Carlos Gonzalez’s two-out walk in the fourth.

“Before the game they said he was Dillon Gee, and that’s exactly what I saw,” Thole said. “Pounded the strike zone.”

Using a big, slow curveball and a fastball from 86-93 mph, McHugh worked out of trouble after the double by Blackmon, who also played high school ball in the Atlanta area. Sacrificed to third, Blackmon was stranded when McHugh threw a called third strike past Jordan Pacheco and fanning Carlos Gonzalez.

“The anticipation is the hardest part, for sure,” he said. “It was trying to contain the nerves. A lot of people gave some really good advice and said you’re going to be nervous. It’s a fact. Just contain those and go out and do your thing.”

Colorado, which tied a season high with its fifth straight win, broke through quickly after McHugh’s departure.

Colvin hit the second pitch from Bobby Parnell (2-3) to straightaway center, where the rookie Valdespin took two steps in, then realized he had misjudged the drive. He backpedaled a half-dozen steps and jumped for a backhand grab, but the ball sailed over his glove.

“The ball jumped off the bat,” Valdespin said.

He’s been a middle infielder for most of his career.

“One of the things you’ve got to be careful of is putting guys out of position in the big leagues, because eventually the ball will find them ,” Collins said. “When you’re in a situation like we are, it’s going to happen at the wrong time, which it has.”

Chris Nelson fouled off a pair of 0-2 pitches, then singled to center past the drawn-in infield.

“I can’t tell you how proud I am of this group,” Tracy said. “Said that many times, it doesn’t take a four-game sweep to say it,”

Rex Brothers (8-2) pitched two innings for the win. Matt Belisle, Colorado’s fifth pitcher, got his first save since June 22, 2010, against Boston following some ninth-inning drama. Pinch-hitter Justin Turner singled leading off and was sacrificed to second by Valdespin. Daniel Murphy flied to center and David Wright flied to right.

“It’s frustrating for everybody,” Thole said. “It’s just not working.”

NOTES: Gold medal-winning American gymnast Gabby Douglas threw out a ceremonial first pitch. It was a high, arching pitch from the front of the mound that was caught to the first-base side of the plate by pitcher Robert Carson. Having not bounced the ball, Douglas raised both arms in triumph. … Murphy is in a 8 for 56 (.143) slide. “He’s out of gas. He’s just flat out of gas, and he need a couple days.” Collins said. … The Mets canceled the option of C Rob Johnson to Buffalo and put him on the 15-day DL, retroactive to Aug. 15, with a ligament tear in his left thumb. … The Mets offered a kids-go-free if accompanied by adults promotion; the game drew 22,544, the 12th-lowest crowd ever at 4-year-old Citi Field.